A corrections officer at the U.S. Penitentiary in Pollock was stabbed in the neck a number of times by an inmate at the facility Monday, officials said Wednesday morning.

The employee was treated at a local hospital Monday night and was released with "relatively minor" injuries, prison spokeswoman Karen Million said. The inmate involved was placed in the facility's special housing unit pending the outcome of an FBI and internal investigation, she said.

The inmate used some type of pointed weapon, and the assault happened around 7:30 p.m. in the housing unit, Million said.

The incident appears to be isolated, but the facility has been placed on lockdown while officials "review operational procedures to ensure staff and inmate safety when we resume normal operations," she said.

This is the first time the facility has been on lockdown since a Jan. 4 assault that left inmate Peter Gutierrez, 55, dead, Million said.

The last inmate-on-staff assault that resulted in injury was in October when an inmate struck a correction's officer in the face, she said.

Since the Jan. 4 homicide at the facility, there have been three inmate-on-inmate "serious assaults," Million said, explaining that a serious assault is one requiring medical treatment or involving some other special circumstances. In each of the three incidents, one person was found guilty of assault in the prison's internal disciplinary process, she said.

Six deaths, one year
In the past year, the facility has had six deaths -- two are still being investigated and may have been from natural causes or suicide; the other four were confirmed assaults.

The most recent death was of Pete Vantha, 36, of Texas, who was found unresponsive March 12 in his cell, Million said. Vantha was transported to a local hospital where he was pronounced dead. He had no obvious wounds, she said, and his death is still under investigation.

Several inmates were being investigated for Gutierrez's Jan. 4 death. Officials said he died from injuries from a homemade weapon.

And an April 20, 2007, assault left Tyrone Johnson, 47, of Washington, D.C., and Derrick Sparks, 25, of Kansas, dead.

Prison surveillance video caught the assault depicting Johnson stabbing Sparks twice, killing him, and then going after Edgar Branch, Sparks' cell mate, officials said. Branch is shown leaving the common area, getting a shank from his cell, a shank from another inmate and strapping one to each hand before going after Johnson, killing him, officials said. Branch has pleaded not guilty to second-degree murder in connection with Johnson's death.

Johnson had been transferred to the prison 18 days before the attack that killed him.

William Bullock, 26, of North Carolina and Donald Till, 32, of Florida both died in a local hospital from wounds suffered from a homemade sharpened weapon on Nov. 15, officials said.

Bullock was stabbed during an altercation with another inmate on that day, officials said, and Till's body was found with stab wounds in the shower after the prison was placed on lockdown. His death is still under investigation.

Till had been at the Pollock prison for just more than a month before his death, and Bullock was there for less than three months.

The last time an inmate was killed in Pollock before the April 2007 homicides was in December 2001 when an inmate killed his cell mate.